Acoustical device



- May 5, 1964 J. H. TODT 3,132,215

ACOUSTICAL DEVICE Filed March 3, 1961 4 Sheets-Sheet 1 INVENTOR. JOACHIM H. TODT ATTORNEY May 5, 1 J. H. TODT 3,132,215

ACOUSTICAL. DEVICE Filed March 3, 1961 4 Sheets-Sheet 2 I2 1 I U D 23 W x 47 1 31 I3 48 m 42 a? as w |5 FIG. 2

INVENTOR. JOACHIM H.TODT W 1.0.

ATTORNEY y 5,1964 J. H. TODT 3,132,215

ACOUSTICAL DEVICE Filed March 3, 1961 4 Sheets-Sheet 3 FIG. 3

IN VEN TOR. JOACHIM H. TODT ATTORNEY May 5, 1964 J. H. TODT ACOUSTICAL. DEVICE 4 Sheets-Sheet 4 Filed March 5, 1961 INVENTOR.

JOACHIM H. TODT ATTORNEY 3,132,215 ACOUSTICAL DEVICE Joachim Herbert Todt, Minneapolis, Minn, assignor to This invention relates to the field of transducers and more particularly to the field of acoustic transducers of the miniature variety.

One of the greatest problems which has confronted manufacturers of acoustic devices such as hearing aids, communications equipment, electronic stethoscopes, and other acoustic communicating devices, has been the problem of obtaining an acoustic transducer which is of miniature size but retains the property of a larger transducer. Hearing aids for instance requirea microphone and re ceiver which have response characteristics that are of espectially high quality in the acoustic range, specifically in the speech range of frequencies. The general trend of michrophone and receiver manufacturers, has been to make them of sufficient size to reproduce (frequencies in the acoustic range with relatively high fidelity but their size has always been restrictive when it comes to placing the units in a confined space such as the space and general shape of the ear canal, as well as in miniature hearing aids. Furthermore, because the microphones and receivers of most hearing aids which are housed in the same structure such as hearing aids worn upon the head,

the relative size of the armature or actuated element within the transducer has been large enough so that vibrations are made through the housing to the microphone causing oscillations and feedback, regardless of the amount of acoustic isolation designed around the microphone and receivers. Also, it is quite evident that certain new techniques are necessary in the manufacturing of acoustic transducers if the miniature type is to be competitive with the larger units. Generally speaking, applying manufacturing techniques for larger units such as telephone receivers and loud speakers as well as different types of microphones, causes difficulties in manufacturing miniature transducers. Not only are the parts more delicate to handle for miniature transducers, but the tolerance between moving pants and other critical function parts hecomes more critical in the miniature type transducer. To accomplish this end, I have employed certain new vacuum deposition and thin film techniques to produce a miniature transducer at a substantially lower cost than that for the larger and bulkier components employed in present day products. While certain techniques of producing thin films by vapor deposition are known to those highly skilled in the art, my teaching of making a miniature thin film transducer is new in the art. Heretofore it has generally been the practice to assemble all the parts of a transducer after each part has ben subjected toall its manufacturing operations, but in practicing my invention, the most delicate part is'assembled while still a part of its supporting form, and the form is removed alter the complete transducer is assembled;

' In present day hearing aids, not only is it desirable to use a miniamre transducer for the michophone and receiver, but it is also highly desirable to produce a transducer which has a much lower cost of production since the microphones and receivers are generally the most expensive components used in a hearing aid :or like item.

It is therefore a general object of my invention to provide an improved transducer which may be used as a microphone or receiver.

It is another object of the present invention to provide a miniature transducer manufactured by vapor deposition and thin film techniques.

United States Patent M It is a further object of my invention to provide a transducer which has a relatively low mass diaphragm.

It is another object of my invention to provide a transducer of inexpensive design without sacrificing quality of performance.

It is another object of my invention to provide a mini aturized transducer which may be easily assembled to maintain close operating tolerances.

It is another object of this invention to provide an instrument using a thin film diaphragm which maybe readily assembled employing new thin film techniques.

These and other features of my invention will become more apparent from the detailed description and accompanying drawings in which like reference numerals refer to like parts, in which:

FIGURE 1 is a cutaway section of my transducer along section lines 6-6 showing the thin film diaphragm position inside the transducer;

FIGURE 2 is a cut-away section of my transducer along section lines 66 showing the diaphragm on a spool before the last manufacturing step takes place;

FIGURE 3 is an exploded view of my transducer show ing all of the parts for the complete assembly;

FIGURE 4 is a sectional view of the spool before the coil is formed thereon;

FIGURE 5 is a cut-away section of the spool showing the coil formed on the diaphragm; and

FIGURE 6 is an end view of the completed assembly showing section lines 6-6 which form a cut-away section of FIGURES 1 and 2.

Referring to FIGURE 1, a transducer 10 is shown which has an outer housing or case 11 that houses the internal components. Case 11 is in the form of a cylinder in which the edges of the cylinder are rolled over or curved such as designated by numeral 12 to form a clamping portion against a pair of cover plates 13 and 14. Cover plate 14 has a plurality of holes 15 cut through the surface of the cover plate, the cover plate having a central portion-forming a stem 16. In like manner, cover plate 13 has a plurality of holes 17 cut through its surface to" provide an acoustic access to the internal structure of the transducer and has a stem portion 20 that has a bore in the stem which receives a male member 21 that is integral with the stern portion 16 of cover plate 14. In other words, cover plates 13 and 14 are essentially identical and are slideably joined together in the center stem portion so that they form substantially a unitary structure when the crimped or rolled over portion 12 of housing 11 engages their outer peripheries. Housing 11 is made of stainless steel (303) and cover plates 13 and 14 are fashioned from chrome steel. Other materials may be used but it must be kept in mind that for certain applications housing 11 may come in contact with the human body and therefore should be perspiration resistant and non-irritant to the body. Cover plates 13 and 14 may be made of other metals having magnetic properties as will be seen later from the description of the rest of transducer 19.

Cover plate 13 has a notch 21 cut in its outer periphery and cover plate 14 has a notch 22 cut in its outer periphery, notches 21 and 22 lying substantially along the same radius from the center of the transducer. Notches 21 and 22 are provided to allow a pair of electrical conductors 23 and 24 to emerge from the internal structure of transducer 10.

Clamped between cover plates 13 and 1d are a pair of ring magnets 25 and 26. Ring magnet 25 has an annular groove 27 cut at its edge which is adjacent to cover plate 14 and has another annular groove 30 cut at the edge opposite cover plate 14. In other words, the cross sec tional area of ring magnet 25 appears to have a T shape Patented May 5, 1964 with the stem of the T pointing inwardly and the cross bar of the T lying adjacent to the outer cylindrical hous ing 11. Ring magnet 26 has an annular groove 31 which is at its edge adjacent to cover plate 13 and has another annular groove 32 on the edge opposite cover plate 13. Ring magnet 26 also takes on the T shape through its cross section. Ring magnets 25 and 26 have their innermost edges abutting each other, that is, the innermost edges of the cross bar portion of the T shape. Ring magnets 25 and 26 are fixedly held in this abutting position by cover plates 13 and 14 due to the crimped or'rolled edges 12 of housing 11.

Situated in annular groove 3%} and 32 is a pair of half washers 33, each of which has a plurality of diametrically spaced holes 34 formed transverse to the plane of the washer, and a central hole 35. Central hole 35 is of sufficient diameter to encircle stem portions 16, 21 and 20 while allowing sufiicient clearance for a coil to ride therein which will be explained more fully later. Half washers 33 are made from chrome steel that is capable of completing a magnetic circuit While ring magnets 25' and 26 are made from elongated single domain iron so that a magnetic path is formed between the abutting surfaces of ring magnets 25 and 26 where like poles are joined in the center of transducer and like poles exist at the outer edge of the transducer adjacent to cover plates 13 and 14. Cover plates 13 and 14 form a magnetic path so that a magnetic pole of the same polarity as found at the outerv edges of ring magnets 25 and 26 exists in the stem portions 16, 21 and 20 of cover plates 13 and 14. Half washers 33 complete the magnetic circuit by being in abutting contact with ring magnets 25 and 26 so that a magnetic pole of polarity opposite that in the stem portions 16, 21 and 20 exist at the innermost edge of central hole 35. In other words, a magnetic circuit is created through ring magnets 25 and 26 and half washers 33 to innermost diameter.

form one leg of a magnetic circuit and through ring 'magnets 25 and 26 through cover plates 13 and 14 having stem portions 16, 21 and 20 forming the other leg of the magnetic circuit with an annular air gap being formed in central hole 35 since stem portions 16, 21 and 20 are centrally located with respect to half washers 33.

A nylon support ring 36 is fastened to half washers 33 by an epoxy 37 cemented at its edge so that it is fixedly secured thereto. Nylon ring 36 has'its outer periphery lying adjacent to the stem portion of the T cross sectional shape of ring magnet 26, nylon ring 36 being of rectarb gular cross section. Situated on the opposite side of half washers 33, is another nylon support ring 40 which has its edge cemented to half washer 33 by epoxy cement 37. Nylon support ring 40 is also of rectangular cross sectional area and has an outer diameter slightly smaller than the inner diameter of the stem portion of ring magnet 25 so that it is tightly assembled against ring magnet 25.

Fastened to the edge of nylon support ring 40 adjacent to cover plate 14, and the edge of nylon support ring 36 adjacent cover plate 13, is a diaphragm 41. Diaphragm 41 has its outer periphery cemented to nylon support ring 40 by an epoxy cement 37 and has a ridged or corrugated annular ring area 42 adjacent to nylon supporting ring 40. Epoxy cement 37 may be of the type manufactured by the Permacel Company of New Brunswick, New Jersey, under the name Per macel Resin 19A. Diaphragm 41 is further described as having a cone shaped portion 43 which is integral with ridged or corrugated rings 42 and extends inwardly towards half washers 33 and central hole 35 to form a tube like portion 44 between half washers 33 and stem portions 16, 21 and 20 which is located in central hole 35. The other portion of diaphragm 41 is formed in like manner and has another outer periphery adjacent nylon supporting ring 36 which is cemented to nylon ring 36 by epoxy cement 37. Also a ridged or corrugated annular ring area 42a is formed which is integral with a cone portion 43a that in turn slopes inwardly towards half washers 33 and central hole 35 to be integrally formed with tube like portion 44. Tube like portion 44 has formedthereon a coil 45 having multiple turns which abut and join cone portions 43 and 43a. Between half washers 33 and coil 45 is a layer of epoxy 37 which covers the plurality of turns of coil 45 and is bonded to the edges of cones 43 and 43a at their In other Words, epoxy 37 forms the supporting portion of tube like section 44 of diaphragm 41 to hold the turns of coil 45 in place and within the air gap between stem portions 16, 21 and 2t) and half washer 33. To complete the electrical circuit to coil 45, leads 23 and 24 are connected to the inner edge of diaphragm 41 in the vicinity of nylon support rings 36 and 40 by an electrical conducting epoxy such as Hysol 10-80 (3507) manufactured by the Hysol Corporation, Olean, New York. This of course requires that the diaphragm 41 be made of a good electrical conductor and generally speaking it is formed from nonmagnetic metals such as aluminum with an anodized surface or such other metals as copper under a tin coating or palladium and chromium on top of a' layer of aluminum. The electrical connection and leads 23 and 24 are coated with a layer of epoxy 37 which has insulating qualities to insulate leads 23 and 24 from contact with the other metal parts. Diaphragm 41 does not touch ring magnets 25 or 26, however, if it is insulated, it will function properly.

In order to develop diaphragm 41, it is necessary to perform several required steps before assembling the transducer. In FIGURE 2, there is shown a spool 46 which is generally made of a plastic material such as acrylic polystyrene or any other suitable material. Spool 46 is much in the shape of a .V-belt pulley having a pair of edges 47 and 48 at the open edges of the V shape. The inner sloped surface of spool 46 is of the same general configuration as described for diaphragm 41 since diaphragm 41 is actually formed on the inner surface of spool 46. Spool 46 may be made by various methods of molding or forming from suitable material and if more convenient may be made in several pieces and then assembled to take on the general formand shape such as shown in FIGURES 2 and 3. In order to form diaphragm 41 it is necessary for spool 46 to be subjected to a series of process steps. The following process should be followed in producing transducer 10, which includes the steps of forming the diaphragm as follows 2 (l) Spool 46 is cleaned by a hot water bath to remove all foreign impurities.

(2) If the surface of spool 46 is somewhat rough or irregular, it should be smoothed by dipping in a lacquer designed for use with vacuum deposition, and one such lacquer is that sold under the name Logo Base Coat, by the Bee Chemical Company. If the spool is sufficiently smooth, this step may be eliminated, but if required, the coating should be about 0.8 to 1.0)(10 inches in thickness.

(3) The spool, with or without the lacquer coating, is

' then put in a desiccator and heat is applied under a vacuum to dry the spool and lacquer, if applied.

(4) The spool 46 is then placed on an arbor between washer like end pieces which project beyond the spool radius and screw threads are turned on the tube like portion 44. Of course it may be possible to mold the screw threads on the spool or form them by. other means. For my invention I have found that approximately 30 screw threads are sufilcient.

(5) The arbor and spool are put in a bell jar and the air is removed so that a vacuum of 10- mm. Hg is defined. The arbor is placed in a jig sot-hat it may be rotated, and a coating of aluminum is deposited by vapor deposition so that all sides of the spool are coated except the covered ends. After the metal has been deposited on the spool and in the screw threads, it will have an appearance in the general area of the tube like structure, (such as shown in FIGURE 4). It will be noted that there is a continuous coating on spool 46 which forms cone portions 43 and 43a as well as the valleys or grooves of the screw threads. The metal which is used should have nonmagnetic properties and have a thickness of between 3 to 5 microns.

(6) The nonmagnetic metal deposited on edges 47 and 48 of spool 46 is removed by the process of scraping or rubbing with an abrasive material so that there is no electrical conducting surfaces on edges 47 and 48 of spool 46.

(7) The outer portion of the screw threads along with the metal deposited thereon is partially ground away so as to form a continuous spiral conductor which forms coil 45. It will be noted that a continuous electrical conductor exists between cone 43 and 43a.

(8) A coating of epoxy 37 is placed under coil 45 so that all of the turns making up the coil are coated with the epoxy and this can best be seen in FIGURE 2. The epoxy is generally from 2 to 3 x 10- inches in thickness moved from spool 46. Leads 23 and 24 are permanently attached to diaphragm 41 by the electrical conducting epoxy.

(9) Epoxy 37 is then applied to nylon support rings 40 and 36 to leads 23 and 24 to cover the electrical conacrylic plastic or polystyrene, it being understood that if spool 46 is made of other readily deformable materials that an appropriate solvent will be used to dissolve spool 46 The solvent used to dissolve spool 46 must be of a com position that does not attack epoxy 37 or the electrical conductive epoxy so that nylon support rings 36 and 40 are cemented to diaphragm 41 and half washers 33, as well as supporting coil between cones 43 and 43a of diaphragm 41. It is also evident that several steps may be reversed in the process of forming the diaphragm and screw threads in the epoxy and vacuum deposit the metal over the epoxy and screw threads. It should also be borne in mind that for certain applications, especially where transducer 10 is used as an acoustic receiver, in transforming electrical waves into sound waves, cone 43 or 43a may take on a, dilferent thickness than the other so that a greater stiffness is formed therein. The particular cone which takes on the thicker dimensions acts as the spider assembly of the traditional loud speaker to provide the proper damping qualities and also aids in keeping the sound producing diaphragm centered between the magnetic poles, thereby keeping coil 45 centered in the magnetic field to give a better quality of sound reproduction.

It will become evident from a study of my specification and drawings that I have shown and described an improved transducer Whi'ch is more easily assembled than present day transducers. It should also be apparent that it is highly impractical and most likely impossible to assemble such a device while the diaphragm is in its fragile form, that is after spool 46 has been dissolved and diaphragm 41 stands alone. Furthermore, since the device may be easily assembled and the last step of completing the transducer, by dissolving spool 46, transducer 10 can be easily stored or shipped-without any damage to diaphragm 41. However, the fact that transducer 10 may be so stored or shipped does not detract from the fact that diaphragm 41 is of such low mass that it will readily stand a high degree of shock and vibration without damage to diaphragm 41. It will also be well known to those skilled in the art that certain variations may be made to my device such as completely closing all of the holes in one cover plate and forming a single orifice in the other cover plate to which a sound conducting tube may be attached. It will also be apparent that one of the cover plates may be formed from material other than a material having magnetic properties and the transducer will still function.

These and other variations and modifications in my invention are Well known to those skilled in the art and I intend in the appended cla1m to cover all such variations and modifications and wish my invention to be limited only by the spirit and scope of the appended claim.

I claim as my invention:

A micro-miniature acoustical transducer for changing one form of energy into another form of energy comprising: a pair of back-to-back cone shaped symmetrical thinfilm metal diaphragms having corrugated outer edges and being formed at the center with a hollow thin-film epoxy tube to connect one diaphragm to the other, said diaphragms being electrically connected through an electrical References Cited in the file of this patent UNITED STATES PATENTS 

